The invention relates to systems for measuring analog signals in general and in particular to measuring systems for high voltage high frequency analog signals.
The prior art is replete with data acquisition systems which utilize digital techniques for accurately and continuously deriving information relative to analog input signals at a plurality of remote stations.
An approach to remotely detecting an analog input signal and faithfully transmitting such information to a receiving station is to use frequency modulation and effect transmission via an optical fiber link. These techniques, however, are not directly applicable to the detection and measurement of high voltage and high frequency signals. One of the main difficulties lies in the hostile environment caused by the high voltage field and by noise interference affecting the quality of the measured signal.
The analog signal to be detected characterizes voltage and current transient phenomena found in 34.5 KV-500 KV transmission lines. The events triggering such transients are unpredictable. Therefore, to capture such transient phenomena a recording system must be on-line at all times. The high voltage field at the measuring point is a constant threat for the electronic components and many noises interfere with the signal. The problems caused by such hostile environment are compounded by the fact that a sophisticated solid state electronic equipment has to be interfaced with equipment which by nature is capable of withstanding high voltages. Such electronic equipment is necessary in order to provide the frequency response and dynamic range imposed by fast front surges due to lightning and line switching transients.
An object of the present invention is to combine high voltage equipment with electronic equipment in a system for recording high voltage, high frequency analog signals derived from a power line.
Another object of the present invention is to provide an improved transmission and detection of such analog signal through frequency modulation to a remotely located measuring station.
Optically-isolated signal transmission lines are known. See for instance "An Automatic Transient Recording System--The CLD Monitor Station" by G. Nourse--a paper presented at the IEEE PES Summer Meeting, Los Angeles, CA, July 16-21, 1978. Broad bandwidth is desirable as well as isolation for remote transmission. An optical link satisfies both requirements. However, the prior art does not teach, except by digital techniques, how such bandwidth requirement can be satisfied at the signal conversion stage, e.g., from an electrical into an optical signal.
Another object of the invention is to measure currents and/or voltages over a frequency range extending from direct current to 100 kilohertz and to transmit such baseband information from the point of measurement to the recording instruments with a minimum of noise or signal degradation.
Lightning surges and switching transients are a recurrent problem for power utilities. It is important to detect and measure such occurrences not only to provide a better protection of the power lines but also to improve the overall network design. Current, or voltage measurement calls for voltage isolation. It is also necessary to provide a remote transmission of analog data to a monitoring or control panel free from the hostile environment.
It is known to derive a measurement of a high tension power line voltage with a capacitor divider coupled to the line at the point of measurement.
A further object of the present invention is to provide a new approach to the derivation of a measurement of high voltages, or currents (for instance, transients and surges) on power lines, such as those due to lightning, and to an improved transmission of the derived signal at a distance from the measurement location.
The invention further bears on reliability, simplicity of design, and cost reduction for measurements in an hostile environment from a remote location. For this purpose, integrated circuit techniques which had been heretofore reserved to digital treatment of signals are used, according to the present invention, in the field of high voltage and/or current measurement including transients and surges.